In the production of products from subsurface bodies, such as the production of petroleum products from kerogen in oil shale, it has been the practice to mine the shale by mechanical means and to retort the shale to temperatures producing chemical changes, hereinafter called pyrolysis of the kerogen. At such temperatures, the kerogen products are largely vaporized or are sufficiently liquid to run out of the pores and fractures in the shale rock to be collected for further processing. Such products at room temperature have substantial portions of high viscosity such that they will not flow, for example, through pipe lines, and they must be treated, for example, by hydrogenation to produce useable, commercially marketable products. The total cost of such processes renders them generally uneconomic.
In addition, such processes produce large amounts of spent shale having components from which undesirable pollutants will be leached by rainfall.
Attempts to process bodies of oil shale in situ by heating the kerogen in the oil shale, for example, injecting superheated steam, hot liquids or other materials into the oil shale formation, have not been economically feasible since, once kerogen is converted to products which flow, large portions of the kerogen were also converted to products which do not flow and which, in fact, could plug the formation since temperatures in some locations exceeded desirable limits, such as 500.degree. C. Attempts to maintain temperature uniformity below 500.degree. C., while still above temperatures such as 250.degree. C. at which the kerogen would pyrolyze at reasonable rates, have been unfeasible since, for example, with steam injected into the formation, thermal conductivity through the shale or kerogen must be relied on to transmit the heat to all portions of the kerogen, and such thermal conduction uniformly heats both the inorganic or mineral portions of the oil shale as well as the organic portion of kerogen in the oil shale.
In addition, since such heat transfer by conduction takes years to bring oil shale up to temperatures where kerogens are pyrolyzed, regions closest to the heat source, having already gasified and liquified, are free to flow through fissures or fractures in the formation, and in a period of years can largely escape from the formation.
For the purposes of this invention, the term, "conductivity", is that given in Dielectric Materials and Applications by A. Von Hippel published by John Wiley & Sons, Pg 4, equation (1.16).